I’ve done a lot of hiking on the south half of the Tuscarora Trail (aka TT) this year. This trail starts at the Appalachian Trail near Matthews Arm campground in the SNP, then travels west through the Massanuttens, and continues north along Great North Mtn and through the Sleepy Creek WMA, before ending at the crossing of the Potomac in Hancock, MD. Up until 1997, this southern half of the TT was known as the Big Blue Trail. It connected with the Tuscarora Trail, which continued north from Hancock, MD to the AT north of Carlisle, PA. However, in 1995, the PATC council and PA Keystone Trail Association agreed to call both sections the Tuscarora Trail; thus, the south half and the north half.
There are a lot of ridge top trails along the TT. This includes sections along Massanutten Mtn, Great North Mtn and Sleepy Creek WMA. These ridgelines are all formed by the resistant sandstone, or quartzite, formations. In fact, virtually all of the ridge tops west of the Shenandoah Valley are formed by quartzites. Not surprisingly, all of these ridge tops have a very similar plant and animal community.
Throughout our mid-Atlantic region west of the Blue Ridge, the rocks that you encounter are basically of three depositional types: limestones, shales, and sandstones (or quartzites, which are sandstones subjected to additional metamorphic pressure). These sedimentary rocks reflect the dynamic level of the inland sea over the past 500 million years, which rose and fell numerous times in response to the emergence or subsidence of the land. Limestones are deposited in shallow seas, while shales, consisting of fine mud particles, are deposited in offshore shallow water conditions, and sandstones most often reflect a beach depositional environment.
In our eastern US, the sandstones/quartzites are the most resistant to erosion, thus, naturally, they will form the ridge tops, while shales; the most susceptible to erosion, will be found in the valleys. Limestones are intermediate in erosion potential. For a good illustration of this, if you look at a map of the Shenandoah Valley, you will notice that the north and south branches of the Shenandoah River cling tight to both sides of Massanutten Mountain. This is because underlying the mountain is the Martinsburg Shale, which extends on both sides of the mountain. The famous ‘Seven Bends’ of the North Branch of the Shenandoah reflects the margins of the soft Martinsburg Shale formation, which entrenches the river within this relatively soft bedrock.
The nature of the bedrock not only affects the topography and drainage basins, but also determines the nature of the soils, which ultimately defines the flora and fauna of any given locale. It does so by it’s tendency to create soils with varying capacity to supply and hold nutrients and water, stabilize pH, and enable the creation of soil structure.
Quartzite formations tend to be beach sands, or similarly formed depositions. As you can imagine, beach sands are generally devoid of organics and nutrients. Additionally, due to their molecular structure, quartzites do not tend to hold much moisture; having more of a tendency to crack, or fracture, thus, limiting the moisture content of the soil. (Quartzite formations are known for rocky talus slopes; a good example being the Erwin formation of the SNP’s southern district.)
The ability to neutralize acid is called buffering capacity. Quartzites have a low-buffering capacity. This means they are extremely subject to becoming acidic, from the inability to buffer the carbonic acids supplied in acid rain. The type of soil and bedrock are very important to buffering capacity (thus, pH and life forms). The amount of carbonate minerals present is the most important factor. If the watershed contains a lot of limestone or dolomite bedrock, it will likely have enough buffering capacity to withstand even the most severe acid rain without any degradation of the environment. On the other hand, if the bedrock in the watershed is mostly quartzite or shale, there may not be enough buffering capacity and the pH will become acidic. The acidification of streams and lakes tends to get worse over time as the buffering capacity in the watershed is depleted. When the pH of the water gets lower, metals in the soil and stream bed become more soluble and dissolve into the water. These metals, especially aluminum, reach levels that are toxic to aquatic life, and this is how acid rain kills the fish.
These same quartzite-derived soils, deprived of nutrients, have a reduced microorganism base. This paucity of animal life, along with the limited plant growth, limits the development of organic humus on quartzite bedrock. It is the organic humus contribution to mineral soils that create the structure of soils, so important to movement of fungus, bacteria and other microorganisms, plant roots, as well as water and oxygen through the soil. In the case of our quartzite soils, the mineral portion of the soil is principally sand, which does not hold water or nutrients. (On the opposite extreme, the shales, consisting mainly of clays, in the absence of organic humus, also have no structure. However, in this case, the clay soil lack the pore space necessary to hold oxygen, and changes from rock hard when dry to highly erodible and slippery when water saturated, creating an a very volatile and inhospitable habitat.)
Thus, our resistant quartzite ridge tops tend to create infertile, dry, and acidic sandy soils. Of course, there are plants that have adapted to this habitat, namely, oaks, pines, and ericaceous acid-loving plants of the heath family, like azaleas, blueberries, huckleberries, rhododendron and mountain laurel. Pink lady slippers also prefer this acidic, well-drained habitat. In fact, the tannins from the oak leaves are acidic in nature, and will continue to ensure that the soils are acidic, self-perpetuating the favorable habitat of the oak forest (Think Gaia.)
One final attribute is associated with our quartzite formations. That would be cliffs. These highly resistant rocks, known to fracture, produce the cliffs of Rip Rap trail, Buzzard Rocks (of Massanutten fame – as well as most other ‘buzzard rocks’), Big Schloss, and, perhaps most well known, Seneca Rocks of WV and North Mtn cliffs.